Yes. 24-70 makes D600 a bit front heavy, but when I hold the camera, I always support the lens with my left hand, so I reckon I've got used to it. When I'm not holding the camera, I will keep it in a bag with the lens pointing down. Thinktank 20 looks good so far.

It may also be large enough to hold the D600 with the longer 70-200mm VR (with ​its​ lens hood reversed) should you ever get that lens, but that won't be a very discreet package.

It should be. I get my D700 with grip and 80-200 in it easily. I've also squeezed the same body with 300f4 and 1.4TC in.

Mama mia, if that's the Thinktank 20, that's not a bag, it's a tank! My largest bag is a Lowepro Toploader 75 AW and it can easily hold a D2x with a 70-200mm VR mounted, but there's no way that it could hold a 300mm f/4 and 1.4x TC. When I think about how large and heavy those loaded bags are, it makes me realize how fortunate I am to not have a 300mm or 400mm f/2.8.

Ha ha ha! I only loaded the 300f4 and 1.4TC combo to see if it would fit, which it did. My usual walk around content for a day outing in a city can end up consisting of a D700 with grip (I just got the D600 when it came out and I'm still learning it but when I do and get the grip for it, it will probably take over in most outings.) with Tokina 12-24, Nikon 35-70 2.8 and 80-200 AF-S. That leaves room for a SB-900, 50 1.8D, a tablet, cords, cards, spare batteries for camera and flash, kitchen sink, Narnia, Jimmy Hoffa was probably in there somewhere.... That's all in just the 20! You can see how it can quickly get out of hand. If I hadn't started backpacking back in the days when pack frames were actually just oxen yokes, I would probably keel over under all of that. If definitely encouraged more stops for a Guinness when I was walking around Dublin all day than if I hadn't had all that gear but when ever is another Guinness a bad thing?!? So there you go, carrying too much junk is actually a good thing.